However, national park trips with wildlife are the exception. I realize that 55-250 is not sufficient for distant wildlife but I'm not interested in sitting on a chair at a viewpoint all day looking for a wolf a mile away.

It's those closer animals I'm interested in.

Clearly, changing lenses without dropiing one or both and keeping the equipment reasonably clean was intended for those with more than two hands. Also, want to be able to change lenses without taking off my backpack and kneeling.

I have a soft-formed LowPro (foam padded and not a pouch) lens case that I can hook to the back of my backpack on one side and have it accessible without taking anything off.

It's the actual process of changing the lens that concerns me. One off the camera. Other out of the case. One into the case. Other onto the camera. Etc.